btrfs_parse_early_options() can fail due to error while scanning devices
(-o device= option), but still strdup() subvol_name string:
mount -o subvol=SUBV,device=BAD_DEVICE <dev> <mnt>
So free subvol_name string on error.
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
        error = btrfs_parse_early_options(data, mode, fs_type,
                                          &subvol_name, &subvol_objectid,
                                          &subvol_rootid, &fs_devices);
-       if (error)
+       if (error) {
+               kfree(subvol_name);
                return ERR_PTR(error);
+       }
 
        if (subvol_name) {
                root = mount_subvol(subvol_name, flags, device_name, data);